Natural User Interfaces (NUI) are supposed to be used by humans in a very logic way. However, the run to deploy Speech-based NUIs by the industry has had a large impact on the naturality of such interfaces. This paper presents a usability test of the most prestigious and internationally used Speech-based NUI (i.e., Alexa, Siri, Cortana and Google's). A comparison of the services that each one provides was also performed considering: access to music services, agenda, news, weather, To-Do lists and maps or directions, among others. The test was design by two Human Computer Interaction experts and executed by eight persons. Results show that even though there are many services available, there is a lot to do to improve the usability of these systems. Specially focused on separating the traditional use of computers (based on applications that require parameters to function) and to get closer to real NUIs.